Rod pumps are commonly used in oil wells to pump well fluid. A typical rod pump secures to a string of production tubing lowered into a well. The pump has a barrel with a plunger that is stroked within the barrel usually by a string of sucker rods extending to a stroking mechanism at the surface. A traveling valve mounts to the plunger, and a standing valve mounts to the barrel below the plunger.
During an up stroke, well fluid that has entered the plunger will be lifted up the production tubing. During the up stroke, the traveling valve is in a closed position and the standing valve is open to allow well fluid to flow into the barrel. During the down stroke, the standing valve closes and the travelling valve is designed to move to the open position to allow well fluid that has entered the barrel to flow into the plunger.
Some wells produce gas as well as liquid. If the well fluid flowing into the barrel contains gas, the plunger will tend to compress the gas during the down stroke. The compression of the gas can result in not enough liquid being in the barrel to push the travelling valve back to an open position during the down stroke. As a result, the pump can become gas locked and cease to pump liquid up the well.
The well pump assembly disclosed herein has a barrel with an axis and is adapted to be suspended in a well. A standing valve seat is mounted in the barrel. A standing valve is carried on the standing valve seat and is movable relative to the standing valve seat between an open position and a closed position. A plunger is carried within the barrel for axial stoking movement. A travelling seat is mounted in a lower end of the plunger. A travelling valve is carried on the travelling valve seat and is movable relative to the travelling valve seat between an open position and a closed position. A magnetic field cooperatively associated with the travelling valve pushes the travelling valve to the open position as the plunger nears a bottom of a stroke.
In the embodiment shown, the magnetic field is provided in part by a travelling magnet carried by the travelling valve for movement therewith. The magnetic field is also provided by a standing magnet carried by the barrel below the travelling magnet. The travelling magnet and the standing magnet have polarities that repel each other, causing the travelling valve to lift from the travelling valve seat as the travelling magnet approaches the standing magnet.
In the embodiment shown, the travelling valve comprises a head and a stem, the stem extending downward from the head through a hole in the travelling seat, the head being landed on the travelling seat while in the closed position. The stem comprises a travelling magnet, defining part of the magnetic field. The stem has one polarity at a lower end of the stem and an opposite polarity at the head. The travelling seat is formed of a non magnetic material;
In the embodiment shown, the stem extends downward horn the head through a hole in the travelling seat. The head lands on an upper side of the travelling seat and blocks the hole while in the closed position. The stem has an outer diameter less than an inner diameter of the hole, enabling well fluid to flow through the hole in an annulus around the stem while the travelling valve is in the open position.
The standing valve may also comprise a standing valve head and a standing valve stem. The standing valve stem extends downward from the standing valve head through a hole in the standing valve seat. The standing valve head lands on an upper side of the standing valve seat while in the closed position of the standing valve. The standing valve seat is also formed of a non magnetic material. In the embodiment shown, the standing valve stem comprises a standing magnet having one polarity at a lower end of the standing valve stem and an opposite polarity at the standing valve head. The polarity of the standing magnet at the head of the standing valve is configured to repel the travelling magnet. A standing valve annulus may surround the standing valve stem in the hole in the standing seat. Well fluid flows through the annulus while the standing valve is in the open position. The standing valve head blocks the annulus while in the closed position of the standing valve.